Hm... Zorn's Lemma is equivalent to Axiom of Choice. Does this mean that we should tag questions about ZL by axiom-of-choice? (Probably not.) Would perhaps Zorn's Lemma deserve a tag of its own. (ZL is a frequently used proof technique.)

But I guess the things about tagging ZL questions are ok as they are now.

I've asked this also in the main chatroom.

@Eugene BTW deleting proof-strategy was suggested here. So if you think that this tag is unnecessary, you should upvote that proposal.